1. Field of Invention
The present invention relates to abrasive tools and process for making same, and more particularly to abrasive wheels suitable for grinding and polishing hard materials, such as metals, ceramics, and composites thereof.
2. Discussion of Related Art
Abrasive tools are commonly used in precision surface grinding or polishing of ceramic, metal, and or composite components. In many grinding operations which utilize abrasive wheels, the thinness, rigidity or stiffness, and surface finish of the cut are important factors. Examples of grinding operations include the dicing, slicing, scribing, slotting, and squaring of silicon wafers and so-called pucks made of alumina-titanium carbide composite for the electronics industry in general, and for the computer industry in particular. As is well known, silicon wafers are processed for integrated circuits, while alumina-titanium carbide pucks are utilized to fabricate flying thin film heads for writing (recording) and reading (playing back) information magnetically stored in computers.
Fine surface finish requirements on the cut surface are commonly achieved by using finer abrasive grits to obtain mirror-like surfaces. Increasing abrasive concentration in the abrasive tool increases stiffness and durability. However, as the concentration of finer abrasives increases in the tool, the number of cutting points significantly increases leading to the generation of high grinding forces. An increase in grinding forces increases heat and tool instability resulting in poor work surface finish. Abrasive tools having a high concentration of fine abrasive grits also typically quickly load with workpiece debris or swarf, which limits permissible cut rates.
Conventional porous abrasive tools, having pores positioned throughout the entirety of the tool, are known. Conventional porous metal composite grinding wheels are commonly formed by processing the metal composite below its necessary time, temperature, and pressure. Conventional porous grinding wheels are also formed by sintering a less well packed metal composite, or by adding hollow glass and ceramic spheres to the composite.
U.S. Pat. No. 6,394,888 to Matsumoto et al., discloses abrasive tools containing high concentrations of hollow filler materials in a resin bond suitable for polishing and backgrinding hard materials.
U.S. Pat. No. 6,685,755 to Ramanath, et al., discloses an abrasive wheel prepared by blending a mixture of abrasive grain, bond material and dispersoid particles. The powder mixture is then pressed into an abrasive laden composite and thermally processed. After cooling, the composite is immersed into a solvent, which dissolves substantially all of the dispersoid particles, leaving a highly porous, bonded abrasive article.
U.S. Pat. No. 6,702,650 to Adefris, discloses a porous abrasive article having a plurality of ceramic abrasive composites bonded together by a binder matrix to form a shaped or irregular abrasive composite used to grind glass and other workpiece surfaces to a mirror finish.
Conventional porous abrasive tools provide a reduced number of cutting points, but may also reduce the overall strength of the tool, and specifically may reduce the strength near an inner diameter of the tool, where tangential stresses are greatest. In addition, controlling the size and shape of porosity in conventional porous tools is difficult, and if hollow spheres are used, it is difficult to prevent crushing the spheres during manufacture. A need remains to provide abrasive tools for cutting and grinding ceramics and other semiconductor materials to mirror-like finishes, having commercially acceptable strength, material removal rates, and wear rates.